Prior-art solutions for a similar purpose include textile projection screens with a reflective surface having a white basic color, thus reflecting all colors. In large spaces and for purposes requiring a large angle of view, projection screens with a dull finish, which are good general-purpose screens, are often used. However, their reflectivity is relatively poor for demanding applications, and therefore they are not well suited for use in bright spaces where there is plenty of diffused light. Metal-coated aluminum or silver screens and so-called iridescent screens give a better reflectivity than dull projection screens, but the problem is a much narrower angle of view. A major problem in the case of all the projection screens described above is encountered in the projection of a dark or completely black color onto the light or white surface of the projection screen. Black portions in the image are areas on which no light is projected at all. All video, motion-picture and slide shows generally look fine in conditions of complete darkness, but when any extra light is admitted into the viewing space, dark portions in the projected image assume a lighter appearance. This extra light is generally called diffused light. The larger the amount of diffused light admitted, the whiter do the dark portions appear, and the image seems to loose contrast. Even in a completely dark room, diffused light is produced when the image is projected onto a white surface. Therefore, on a prior-art projection screen, the image has a poor contrast because black portions of the image are the same color with the white screen. In spaces containing diffused light, normal contrast is achieved by increasing the brightness of the image, which again causes strain of spectators' eyes while also producing more diffused light, thus further weakening the contrast.
A solution disclosed in U.S. Pat. No. 5,864,426 aims at improving color distribution in a projected video image by increasing the reflection of the blue light component. This is implemented by providing the screen with blue reflective elements placed at even distances among the white standard reflective elements, thus improving the reflection of blue light and correspondingly reducing the reflection of red and green light. This solution, too, has the drawback that, while producing a bright image with a good color distribution, it cannot produce the black portions of the image correctly. Since most of the reflective elements in this projection screen, too, are white, black portions of the video image mainly look white.
U.S. Pat. No. 5,193,015 also discloses a solution dealing with the problem caused by diffused light. It comprises a reflector element consisting of a number of superposed layers, two of which are designed to reflect red color, two to reflect green color and two to reflect blue color. The reflector element additionally contains other layers. The solution disclosed in this patent is actually not a textile projection screen but a liquid crystal operated reflector element, which is very expensive as compared with a textile projection screen, especially when implemented in a large size. In addition, a reflector element of this type is considerably more susceptible to damage than the projection surface of the present invention, which may be e.g. a textile projection screen or equivalent.